A thermal CVD (Chemical Vapor Deposition) apparatus comprises a furnace. According to the thermal CVD apparatus, a plurality of raw material gases are mixed and allowed to flow into in the furnace, and a film is formed on a substrate. If the film is formed on the substrate, the film adheres not only to the substrate but also to an inner side of the furnace. If the film adhering to the inner side of the furnace is accumulated and becomes thicker, the film is peeled off, and this generates foreign material.
To avoid this, etching gas is allowed to flow at regular intervals, and cleaning is carried out to remove the film on the inner side of the furnace. When the film is SiN for example, DCS (SiH2Cl2: dichlorsilane) gas and non-plasma NH3 gas are used as the raw material gas, and gas including F (fluorine) such as NF3 and ClF3 is used as the etching gas.
The film on the inner side of the furnace is removed by the cleaning, molecules including F (F component, hereinafter) adsorbs and bonds to the inner wall surface of the furnace and remains thereon immediately after the cleaning. The molecules are separated at the time of subsequent film forming operation onto the substrate and hinder the film formation, and the film forming speed is decreased. This is because that F has etching function, F reacts with Si of an SiN film formed on the substrate to form SiF4 (gas), and Si is removed from the substrate. Another reason is that F reacts with reaction gas (DCS), and an amount of raw material gas is reduced.
For this reason, in the conventional thermal CVD apparatus, after the cleaning and before the film is formed on the substrate, the film is forcibly deposited on the inner side of the furnace. This is called film-preformation. With this film-preformation, F component is allowed to react with the raw material of the film or is encapsulated under the film (this is also called trap of F component) so that F component is reduced from an atmosphere in the furnace as much as possible and the film forming speed is recovered when a film is formed.
In recent years, SiN films can be formed also by an ALD (Atomic Layer Deposition) apparatus. In the ALD apparatus, DCS gas and NH3 activated by plasma (also called NH3 plasma or NH3 radical) are used as the reaction gases, and these two reaction gases are alternately supplied and films are formed one atom layer by one atom layer. If the ALD apparatus is used, even at low temperature, it is possible to form a high quality film as high as that formed by the thermal CVD apparatus which requires high temperature process. However, even with the ALD apparatus, a film must be preformed after cleaning to remove the remaining F like the thermal CVD apparatus.
In the above-described conventional technique, elements including the cleaning gas are trapped by the film-preformation, and the elements are eliminated from an atmosphere in a reaction container as much as possible. For this purpose, it is necessary to carry out the film-preformation. Further, even if a thick film-preformation is carried out, the elements included in the cleaning gas can not effectively be eliminated from the atmosphere in the reaction container. Further, since it is necessary to add a thermal CVD film-forming nozzle in addition to a special-purpose buffer nozzle, the structure of the reaction container becomes complicated and costs thereof are increased. If the thermal CVD film-forming nozzle is added, there is a problem that foreign materials are generated due to film formation in the CVD film-forming nozzle, and this is not preferable.
Therefore, it is a main object of the present invention to provide a substrate processing apparatus capable of effectively eliminating elements included in cleaning gas.
It is another object of the invention to provide a substrate processing apparatus capable of effectively preventing foreign materials from generating from a gas supply system, and to eliminate the need of the gas supply system itself.